Moisture resistant, flexible epoxy/cyanate ester formulation

ABSTRACT

Compositions having high moisture resistance and flexibility comprise an organic component and a filler. The organic component comprises a long-chain cycloaliphatic epoxy resin, a short-chain cycloaliphatic epoxy resin, a cyanate ester, and a lewis acid catalyst. Preferably the organic component further comprises a bronsted acid co-catalyst and/or a flexibilizing modifier. The compositions are useful in various semiconductor applications, including as die attach adhesives, underfills, encapsulants, via fills, prepreg binders, polymer solder masks and polymer bumps on flip chip or BGA assemblies.

BACKGROUND OF THE INVENTION

The present invention relates to a resin composition useful in theformulation of die attach adhesives, encapsulants, underfills, viafills, prepreg binders, polymer solder masks and polymer bumps on flipchip or BGA assemblies.

As uses for semiconductor devices continue to increase, there is agrowing demand for adhesive compositions and resin formulations usefulin the packaging of such devices both on the board and substrate level.Adhesives are used, for example, to attach dies to semiconductorpackages under a variety of conditions. Underfills are used to reducestress and increase the reliability of solder ball joints found betweenthe substrate, i.e., package, and the die. Encapsulants are used tocompletely encapsulate, seal and bond a die to a semiconductor package.Via fills are used in both board and laminate substrates to fill thevias in the substrate. Binders found in the manufacture of printedcircuit boards and laminate substrates are needed as part of thestructural composite of the laminate, serving to bind various metallayers and circuitry together into a single functioning unit. Thealternating layers of circuitry, metal planes and vias, along with amatte material, such as glass fibers (which help with structuralintegrity), are bound together with the organic polymer binder to createthe total laminate. Simple layered structures of glass and binder areoften sold in a pre-cured state call “prepregs”, which are laterhead-bonded or laminated together as part of the process that createsthe laminate substrate or printed circuit board.

To be useful in the manufacture of semiconductor devices, die attachadhesives and the like must meet certain performance, reliability andmanufacturability requirements as dictated by the particularapplication. Performance properties for which there are typicallyminimum requirements include adhesion, coefficient of thermal expansion,flexibility, temperature stability, moisture resistance and the like.Reliability requirements are typically evaluated by the device'ssensitivity to moisture-induced stress. Manufacturability requirementsgenerally include specific requirements for rheology, cure rates andusable pot life and the like. For both the via fill and laminatestructures, properties must be met that exhibit superior dimensionalstability to processes such as plating, machining, sanding and baking.

Moisture resistant and flexible materials are highly desirable for themanufacture of semiconductor devices. Moisture inside a package turns tosteam and expands rapidly when the package is exposed to hightemperatures (for instance during solder reflow, infrared or convectionbaking, or if the package is contacted by molten solder). Under certainconditions, moisture induced pressure will initialize package failuresuch as internal delamination in the interfaces, internal cracking, wirenecking, bond damage, and of course the obvious external crack i.e.popcorning.

Resin compositions comprising a cyanate ester and epoxy resins have beendemonstrated to be useful as die attach adhesives, underfills, and thelike. While the performance characteristics for such resin compositionsare adequate for some applications, there is a continuing need toimprove reliability and manufacturing performance of the compositions.Currently available compositions address some, but not all, of thefollowing performance criteria: long pot life, fast cure, and highadhesion. Currently available materials tend to exhibit high rigiditywith a Young's modulus of 4-7 GPa at room temperature and low moistureresistance. A need therefore exists for compositions that exhibitadequate flexibility while providing sufficient moisture resistance.

SUMMARY OF THE INVENTION

In one embodiment, the present invention is directed to a compositioncomprising an organic component and a filler, wherein the organiccomponent comprises at least one long-chain cycloaliphatic epoxy resin,at least one short-chain cycloaliphatic epoxy resin, at least onecyanate ester, and at least one lewis acid catalyst. Preferably thecomposition further comprises a bronsted acid co-catalyst and/or aflexibilizing modifier.

In another embodiment, the invention is directed to a method forpreparing a die attach adhesive comprising preparing a formulationcomprising a composition as described above, dispensing the formulationonto a substrate, and curing the formulation.

In still another embodiment, the invention is directed to a method forpreparing an underfill comprising preparing a formulation comprising acomposition as described above to a rheology suitable for dispensingpurposes, dispensing the formulation onto a substrate, and curing theformulation.

In yet another embodiment, the invention is directed to a method forpreparing an encapsulant comprising preparing a formulation comprising acomposition as described above, dispensing the formulation onto anelectrical component, and curing the formulation.

The invention is also directed to a method for preparing a via fillcomprising: preparing a formulation comprising a composition asdescribed above, printing the formulation into one or more holes in asubstrate, and curing the formulation.

Additionally, the invention is directed to a method for preparing aprepreg binder comprising preparing a formulation comprising acomposition as described above, impregnating the formulation into amatte, and B-staging the formulation.

Another aspect of the invention is a method for preparing a polymersolder mask comprising preparing a formulation comprising a compositionas described above and at least one catalyst capable of serving as aphotoinitiator, applying a film of the formulation onto a substrate toform a formulation-coated substrate, photoimaging the formulation-coatedsubstrate, curing the formulation, and developing the formulation-coatedsubstrate.

Yet another aspect of the invention is a method for preparing polymerbumps on a flip chip or BGA assembly comprising preparing a formulationcomprising a composition as described above, printing the formulationonto a substrate to form polymer bumps, B-staging the formulation,contacting the polymer bumps with a bond pad to form an electricalcontact, and curing the formulation onto the bond pad.

DETAILED DESCRIPTION OF THE INVENTION

In one embodiment, the present invention is directed to a compositionparticularly suitable for die attach adhesives, underfills and the like.The composition comprises an organic component and a filler. The organiccomponent comprises a long-chain cycloaliphatic epoxy resin, ashort-chain cycloaliphatic epoxy resin, a cyanate ester, and a lewisacid catalyst.

One or more long-chain cycloaliphatic epoxy resins are included toimpart flexibility to the composition. A long-chain cycloaliphatic epoxyresin is one having a long chain containing at least 4 carbon atomsbetween the cycloaliphatic groups. Preferably the long chain does notcontain any cyclic groups. Particularly suitable long-chaincycloaliphatic epoxy resins useful in the present invention include, butare not limited to, bis[3,4-epoxy-cyclo-hexyl-methyl]-adipate (CAS #3130-19-6) (for example, that sold under the trademark ERL4299 by UnionCarbide of Danbury, Conn.), and cycloaliphatic mono- and di-epoxyoligosiloxanes such as α,ω-di-(3,4 cyclohexene-2-ethyl)-tetramethyldisiloxane,α,ω-di-(3,4 cyclohexene-2-ethyl-hexamethyl trisiloxane, andα-3,4-cyclohexene-2-ethyl pentamethyldisiloxane (these resins can beobtained, for example, as described in J. Poly. Sci. Poly. Chem.,28:479-502 (1990), the disclosure of which is incorporated herein byreference), and the proprietary cycloaliphatic epoxy resin compositionssold under the tradenames UVACURE 1562, UVACURE 1500, UVACURE 1501 (UCBChemicals, Smyrna, Ga.). The total amount of long-chain cycloaliphaticepoxy resins in the composition preferably ranges from about 5% to about20% by weight, more preferably about 12% to about 15% by weight, stillmore preferably about 13.4% by weight, based on the total weight of theorganic component.

One or more short-chain cycloaliphatic epoxy resins are included in thecomposition which help to increase temperature resistance and reducebleeding of the formulation. A short-chain cycloaliphatic epoxy resin isone having a short chain between the cycloaliphatic groups with theshort chain containing 3 or less, preferably 2 or less, carbon atoms.Particularly suitable short-chain epoxy resins for use in the presentinvention include, for example, (CAS # 2386-87-0) (for example, thatsold under the trademark ERL4221 by Union Carbide). Other usefulshort-chain epoxy resins include, but are not limited to, vinylcyclohexene dioxide (available, for example, from Aldrich, Milwaukee,Wis.), vinyl cyclohexene monoxide (sold by Union Carbide under thetradename ERL420b), and 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxycyclohexane meta-dioxane (sold by Union Carbide under the tradenameERL-4234), and the proprietary cycloaliphatic resin compositions soldunder the tradenames UVACURE 1562 and UVACURE 1533 (UCB Chemicals,Smyrna, Ga.). The total amount of short-chain cycloaliphatic epoxyresins in the composition preferably ranges from about 10 to about 35%by weight, more preferably about 25% to about 29% by weight, still morepreferably 26.9%, based on the total weight of the organic component.

One or more cyanate esters, in combination with the cycloaliphatic epoxyresin(s), impart both adhesion and moisture resistance to thecomposition due to the highly aliphatic nature of the epoxy as well asdue to the formation of cross-product species such as isocyanurates andoxazolidones. These cyanate esters have one, and preferably two or more,isocyanate (—OCN) functional groups. They can be monomer or oligomers,preferably with a molecular weight ranging from 100 to 2000 dependingupon final application. Particularly preferred cyanate esters for use inthe present invention include, but are not limited to,1,1′-bis[4-cyanatophenyl]ethane (for example, that sold under thetrademark AroCy L-10 by Ciba Geigy),bis(4-cyanato-3,5-dimethylphenyl)methane (available from Ciba Geigy),and 1,3-bis(cyanatophenyl-1-(1-methylethylethylidene))benzene (availablefrom Ciba Geigy). The cyanate ester is preferably present in thecomposition in an amount ranging from about 30 to about 50% by weight,more preferably about 37% to about 43% by weight, still more preferablyabout 40.2% by weight, with respect to the total weight of the organiccomponent.

Also included in the composition is a lewis acid catalyst. It has beenfound that the use of a wear lewis acid catalyst produces improvedreactivity and product distribution over other metal catalysts.Preferred lewis acid catalysts for use in the present invention include,but are not limited to, compositions comprising titanium-basedcompounds, such as titanium (IV) isopropoxide, titanium (IV) butoxide,titanium (IV) ethoxide, chlorotitanuim (IV) triisopropoxide, titanium(IV) propoxide, titanium diisopropoxide bis(2,4-pentanedione), titanium(IV) cresylate, titanium (IV) bis (acetoacetonate)diisopropoxide,titanium (IV) oxide acetylacetonate, titanium 2-ethylhexoxide,organo-tin compounds such as tributyl(ethyl)tin,tributyl(1-ethoxyvinyl)tin, tributyl(hexylethyneyl)tin, trimethylphenyltin, tetrabutyl tin, and bis-(2-ethylhexanoyloxy)bis-(2ethylhexyl)tin(all available from Aldrich); and zirconium-based compounds such aszirconium (IV) acetylacetonate (available from Aldrich), zirconium (IV)neoalkanolato, tris(neodecanto-O) (such as Ken React NZOl available fromKenrich Petrochemicals, Bayonne, N.J.), zirconium (IV) neoalkanolato,tris(diisooctyl)pyrophosphato-O (such as Ken-React NZ38), zirconium (IV)bis octanolato cyclo (dioctyl) pyrophosphato-O,O (such as Ken-React KZOPPR) and zirconium (IV) ethylhexanoate; tantalum-based compounds (suchas those available through Gelest, Tullytown, Pa.); borane-aminecomplexes such as tertbutylamine (available, for example, from Aldrich);boron complexes, such as the proprietary composition sold under thetradename DY9577 (Ciba-Geigy); and vanadium-based catalysts (such asthose available through Gelest). In additional, stronger lewis acids,such as boron halides, amino complexes of boron halides and aluminumhalides can be used. Preferably the lewis acid catalyst comprises atitanium-based compound or a zirconium-based compound. The lewis acidcatalyst is preferably present in the composition in an amount rangingfrom about 0.4% to about 0.8% by weight, more preferably about 0.5% toabout 0.7% by weight, still more preferably about 0.7% by weight, basedon the total weight of the organic component.

The filler can be any suitable filler known in the art, such as metalflakes and powders and inorganic powders. Examples of suitable fillersinclude, but are not limited to, silver, gold, copper, conductivepolymers (such as Eeonomer, available through Eeonyx, Pinol, Calif.),boron nitride, aluminum nitride, alumina, silica, silicon nitride,silicon carbide, graphite, and diamond. The filler is preferably presentin the composition in an amount ranging from about 50% to about 90% byweight based on the total weight of the composition. Where the filler isan electrically conductive metal filler, such as silver, gold or copper,it is present in the composition in an amount preferably of about 65% toabout 90%, more preferably about 70% to about 80%, still more preferablyabout 80%, by weight. Where the filler is a non-conductive filler, suchas silica or alumina, preferably it is present in the composition in anamount of about 50% to about 65%, more preferably about 58% to about62%, still more preferably about 60%, by weight.

In a preferred embodiment, the organic component of the inventivecomposition further comprises one or more bronsted acid co-catalysts,which promote rapid chemical reaction at a relatively low temperature.Preferably the bronsted acid co-catalyst is a weak bronsted acidcatalyst, i.e., having a pKa greater than or equal to about 4.Particularly preferred bronsted acid co-catalysts useful in the presentinvention include, but are not limited to, phenol-based molecules, suchas catechol, 4-nitrosophenol, tert-butylphenol, 2,3-dimethoxyphenol,2,6-dimethyl-4-nitrophenol, bisphenol A, 4-(4-nitrophenylazo)catechol,4-methylcatechol, ethoxylated nonylphenol acrylate, and nonylphenol;beta diketonates (such as benzoylacetone and dibenzoylmethane), diesters(such as ethyl malonate), and ketoesters (such as ethyl acetoacetate).The bronsted acid co-catalyst is preferably present in the compositionin an amount ranging from about 0.3 to about 0.8% by weight, morepreferably about 0.5% by weight, based on the total weight of theorganic component of the composition.

In a particularly preferred embodiment, the organic component alsocomprises one or more flexibilizing modifiers. Preferred flexibilizingmodifiers for use in the composition include, but are not limited to,functionalized flexible long-chain compounds, such as epoxy-terminatedsiloxanes, epoxy/hydroxy functiondized poly butadiene (available, forexample, from Aldrich) and epoxidized oils, such as epoxidized methyllinseedate (for example, Vikoflex 9010, sold by Elf Atochem,Philadelphia, Pa.) and long-chain functionalized double-bondedcompounds, such as acrylates and rubbers, for example, urethaneacrylates (such as those sold under the names CN 953 and CN 980 bySartomer Co., Exton, Pa., and Ebecryl 8402 by UCB Chemicals, Smyrna,Ga.) and methacrylated polybutadiene acrylonitrile (such as those soldunder the names Echo Resin MBXN 327 by Echo Resins and Lab., Versailles,Mich., and Ebecryl 3604 from UCB Chemicals). As used herein, the term“functionalized” refers to compounds that are polymerizable under acatalyst and cure temperature of the present system or compounds thatare capable of allowing free radical initiation by peroxides, azo-typeinitiators or other free radical sources. The flexibilizing modifier ispreferably present in the composition in an amount ranging from about 5to about 25% by weight, more preferably from about 16% to about 20%,still more preferably about 18% by weight, based on the total weight ofthe organic component.

The present compositions can contain additional components, as known tothose skilled in the art. For example, the compositions can contain ananti-chain transfer agent or a free radical initiator.

The compositions of the present invention are particularly useful in themanufacture of semiconductor devices. Specifically, the resincompositions of the present invention are useful in formulating dieattach adhesives, underfills, encapsulants, via fills, and binders for aprinted circuit board laminant.

Die Attach Adhesives

Die attach adhesives are used to attach semiconductor chips, i.e., tolead frames. Such adhesives must be able to be dispensed in smallamounts at high speed and with sufficient volume control to enable theadhesive to be deposited on a substrate in a continuous process for theproduction of bonded semiconductor assemblies. Rapid curing of theadhesives is very desirable. It is also important that the curedadhesives demonstrate high adhesion, high thermal conductivity, highmoisture resistance and temperature stability and good reliability.

Conductive die attach adhesives prepared in accordance with the presentinvention comprise the resin composition of the present invention,including at least one conductive filler. For thermally conductiveadhesives (without electrical conductivity) non-conductive fillers suchas silica, boron nitride, diamond, carbon fibers and the like may beused. In addition to the electrically and/or thermally conductivefiller, other ingredients such as adhesion promoters, anti-bleed agents,rheology modifiers, and the like may be present.

Typical steps in the preparation of a die attach adhesive includepreparing the uncured formulation to a rheology typical for dispensepurposes, dispensing the formulation onto a suitable substrate, placinga die on top of the formulation to set a bond-line, and curing theformulation. Suitable substrates include, for example, ceramic,gold-plated ceramic, copper leadframes, silver-plated copper leadframes,laminant substrates, (such as copper-, silver- or gold-plated laminantsubstrates), and heat slugs (such as copper heat slugs and silver-coatedheat slugs).

Encapsulants

Encapsulants are resin compositions that are used to completely encloseor encapsulate an electronic component. An encapsulant prepared inaccordance with the present invention comprises the resin composition ofthe present invention, including non-conductive fillers such as silica,boron nitride, carbon filer and the like. Such encapsulants preferablyprovide excellent temperature stability, e.g., are able to withstandthermocycling from −65° C. to 150° C. for 1000 cycles; excellenttemperature storage stability, e.g., 1000 hours at 150° C.; supplyexcellent protection against moisture e.g., are able to pass a pressurecooker test at 121° C. at 14.7 psi for 200 to 500 hours with nofailures; and are able to pass a HAST (highly accelerated stress test)test at 140° C., 85% humidity at 44.5 psi for 25 hours without anyelectrical mechanical failures.

Typical steps in the preparation of a liquid encapsulant includepreparing a formulation, dispensing (e.g., syringe dispensing) theformulation on the top of the electronic component, and curing theformulation.

Underfills

Underfill materials are used in flip-chip devices to fill the spacebetween the flip chip and substrate. The underfill materialenvironmentally seals the active surface of the flip chip as well as theelectrical interconnections. It also provides an additional mechanicalbond between the flip chip and the substrate and prevents excessivestress on the small electrical interconnects between the chip and thesubstrate. The underfill material is typically an epoxy resin with inertfillers. The viscosity is adjusted to provide proper flowcharacteristics to allow complete filling of the space.

Typical steps for preparing an underfill include preparing the uncuredformulation to a rheology typical for dispensing purposes, dispensingthe formulation onto the substrate, and curing the formulation.Depending upon the application, the formulation rheology is adjusteddepending upon whether the underfill is edge-dispensed for capillaryflow or syringe-dispensed for a no-flow underfill process.

Via Fills

Via fills are used to fill the vias in the substrate. The vias formelectrical or thermal conductive pathways in the substrate. Filling thevias is necessary to maintain the dimensional stability of thesubstrate. The via fill material preferably contains a conductive fillerthat will be either metal or inorganic filled, depending upon the needfor electrical and/or thermal conductivity. In addition the filler willact as part of the structural stability of the material againstexpansion or shrinkage during steps such as plating, baking, machining,drilling, sanding or sawing. Advantageously, the via fill material hasgood adhesion to both metal and laminate layers as well as good moistureresistance.

Typical steps in preparing a via fill include preparing an un-curedformulation, preferably in the form of a paste of high viscosityadequate for screen or stencil printing, printing the formulation intothe holes of a substrate, and curing the formulation.

Prepreg Binders

Prepreg binders are used to create the laminant structure used inprinted circuit boards and semiconductor laminate packages. Thestructure typically consists of alternating layers of metal planes;metal circuit patterns and prepreg. Generally, the prepreg laminantlayers comprise a structural material matte (e.g., a glass matte), andthe binder is impregnated in the matte. Binder material advantageouslyhas high moisture resistance, has high adhesion to the glass matte andto the subsequent metal layers used, has high Tg, has high strength, andis capable of machining without cracking, peeling or shatter.

Typical steps in the preparation of a prepreg binder include, preparinga formulation as described above, impregnating the formulation into thematte, and B-staging (i.e., partial curing) the formulation. Once theprepreg binder is prepared, circuitry or other structures (vias, groundplanes, etc.) are formed on the matte, and one or more matte structuresare laminated at high temperature.

Polymer Solder Masks

Another use for the formulations according to the invention is as amoisture-resistant solder mask. Solder masks are photo-imagablematerials that are used to define circuitry on packages. Becausemoisture-resistance is a point of failure for many solder masks, thehigh moisture-resistance of the polymer is needed.

Typical steps in the preparation of a solder mask include preparing anun-cured formulation comprising one or more catalysts that are capableof serving as photo-initiators (including free radical initiators andmetal-based radical cation lewis acid initiators), applying a thin filmof the formulation to a substrate (e.g., a laminate substrate) to form aformulation-coated substrate, which may involve web, stencil or screenprinting or meniscus or spin coating, photoimaging theformulation-coated substrate, curing the formulation, and developing theformulation-coated substrate.

Polymer Bumps on a Flip Chip Assembly or on a BGA Assembly

Another use of the formulations according to the invention is as amoisture-resistant system for polymer bumps used in a flip-chip assemblyor a BGA (balt grid array) assembly. The polymer bumps replace typicalsolder bumps and must be highly electrically conductive.

Typical steps in the preparation of polymer bumps include preparing aformulation to the application rheology, printing (e.g., stencil-,screen- or jet-printing) the formulation onto a substrate (e.g., asilicon die), B-staging the formulation, contacting the polymer bumpswith a bond pad to form an electrical contact, and curing theformulation to the bond pad.

The compositions of the present invention are preferably cured at a curetemperature of at least about 130° C. for about 1 hour. More preferably,the compositions are cured at a cure temperature of about 175° C. forabout a half hour. As used herein, a polymer is said to be “cured” whenuseful mechanical strength and adhesive properties are developed. Forexample, dicyanate monomers develop useful polymer properties when about85% or more of the cyanate functional groups have reacted to formtriazine rings.

The compositions of the present invention can be prepared by any methodknown to those skilled in the art. A preferred method for preparing theinventive compositions involves first combining the long-chaincycloaliphatic epoxy resin(s), the short-chain cycloaliphatic epoxyresin(s), and the cyanate ester(s). If included in the composition, thebronsted acid co-catalyst and/or the flexibilizing modifier are alsoadded at this time. These components are all mixed, preferably undervacuum, preferably at a temperature of about 60° C. The components aremixed until a homogenous, transparent mixture is obtained, preferablyfor about 30 minutes. The mixture is cooled to a temperature rangingfrom about 10° to about 25° C., more preferably to about 15° C. Thelewis acid catalyst is then added to the mixture. The mixture is set ata temperature of from about 15° C. to about 25° C., more preferablyabout 15° C., and is mixed, preferably under vacuum for about 30minutes. The filler is then added to the mixture, which is mixedfurther, preferably under vacuum for about one hour at 85 r.p.m. andpreferably at a temperature of about 25° C. The mixture should then bestored at a temperature ranging from about −40° C. to about −25° C.,more preferably about −40° C.

EXAMPLE 1

The following compositions according to the invention were prepared in amanner similar to that described above, with the weight percent of eachcomponent indicated, based on the total weight of the composition, andthe physical properties provided in Table 1. Composition 1bis[3,4-epoxy-cyclohexylmethyl]-adipate 2.7% ERL4299 (Union Carbide,Danbury, Connecticut) 3,4-epoxy/cyclohexylmethyl-3,4/epoxy cyclonexanecarboxylate 5.4% ERL4221 (Union Carbide, Danbury, Connecticut)1,1′-bis[4-cyanatophenyl]ethane 8.0% AroCy L-10 (Ciba Geigy, Brewster,N.Y.) catechol 0.2% titanium 2-ethylhexoxide 0.1% epoxidizedhydroxylated polybutadiene 3.6% silver filler  80% PM4130 (JohnsonMatthey, San Diego, CA) Composition 2bis[3,4-epoxy-cyclohexylmethyl-adipate] 7.2% ERL4299 (Union Carbide,Danbury, Connecticut) 1,1′-bis[4-cyanatophenyl]ethane 7.2% AroCy L-10(Ciba Geigy, Brewster, N.Y.) catechol 0.09%  titanium 2-ethylhexoxide0.1% 1,6-dicyanohexane 0.4% D7800-8 (Aldrich Chemical Co., Milwaukee,WI) hydantion epoxy resin: 2,4-imidazolidinedione-5-ethyl-5-methyl-1,3-bis(oxiranylmethyl) 0.61%  Araldite AY 238 (Ciba-GeigyCorp., Brewster, NY) modified acrylated bisphenol A epoxide 99% + 0.9%Echo Resin AE-371 (Echo Resins & Lab., Versailles, MI) polyethyleneglycol (400) diacrylate 0.96%  SR344 (Sartomer Co., Exton, PA) aliphaticurethane acrylate 2.24%  CN953 (Sartomer Co., Exton, PA) mixture ofAroCy L-10 (96.7%) and dibenzoyl peroxide 0.3% (Lucidol-98, Elf Atochem,Philadelphia, PA) (3.3%) silver filler  80% PM4130 (Johnson Matthey, SanDiego, CA)

TABLE 1 Physical Properties Typical Properties Composition 1 Composition2 Filler (Silver) 80% 80 Specific gravity 4 gm/cc 4 gm/cc Viscosity @40s⁻¹ 11 Pas 12 Pas Pot life >8 hrs >8 hrs Recommended cure 175° C./30min 175° C./30 min profile or or 150° C./1 hr 150° C./1 hr ElectricalVolume 0.005 0.005 Resistivity Ωcm Die shear strength 19 kg on 19 kg on(80 ×80 mil die) Ag spot Cu Ag spot Cu PLCC leadframe PLCC leadframeWater absorption 0.11% 0.19% (in 100° C. boiling water/2 hrs)Hydrolisable ionic Cl⁻= 2 ppm, Cl⁻= 2 ppm, contents F⁻< 1 ppm F⁻< 1 ppm(Parr bomp K⁺= 3 ppm, K⁺= 3 ppm, 121° C./16 hrs) Na⁺< 1 ppm Na⁺< 1 ppmGlass Transition 151° C. 140° C. Temperature (DMA method) Young'sModulus 0.97 GPa @ 30° C. 0.90 GPa @ 30° C. 0.072 GPa @ 240° C. 0.06 Gpa@ 240° C. ROC (600 × 600 mil 0.5 m 0.7 m die on Cu foil) Weight lossduring 0.22@ 20-200° C. 0.31@ 20-200° C. cure % 0.47@20-250° C.0.54@20-250° C. Coefficient of thermal 52 in/in/° C. 50 in/in/° C.expansion Voiding <0.2% before cure <0.2% before cure <0.5% after cure<0.5% after cure Storage life 6 months 6 months (@−40° C.)

Compositions 1 and 2 were tested, along with several commerciallyavailable compositions, as described below in Tables 2 to 7. TABLE 2Moisture Resistance after 85/85* precondition on BGA substrate (Diesize: 80 × 80 mil; Substrate: BGA laminate with solder mask on surface)*85/85 test: Expose unencapsulated specimen in 85% relative humidity and85° C. for 168 hr. and then pass solder reflow at 220° C. for 1 min. Dieshear Die shear Adhesion strength before strength after retention afterMaterial condition (kg) condition (kg) condition (%) JM2500* 6.2 2 32.2JM7100* 4.2 4 95.2 JM2801* 9.1 5.1 56.0 QMI505† 8.9 9.6 107.9 Ablebond8360‡ 13.6 13.9 102.2 Composition 1 6.2 9.8 158.1 Composition 2 5.2 2.140.4*Commercially available from Johnson Matthey, San Diego, CA†Commercially available from Quantum Materials, Inc., San Diego, CA‡Commercially available from Ablestik, Rancho Dominguez, CA

TABLE 3 Moisture Resistance after 85/85* precondition on PLCC substrate(Die size: 80 × 80 mil; Substrate: PLCC silver coated copper leadframe)*85/85 test: Expose unencapsulated specimen in 85% relative humidity and85° C. for 168 hr. and then pass solder reflow at 220° C. for 1 min. Dieshear Die shear Adhesion strength before strength after retention afterMaterial condition (kg) condition (kg) condition (%) JM2500 17.5 12.470.9 JM7100 2.5 4.1 164 JM2801 7.0 3.4 48.6 QMI505 12.6 6.7 53.2Ablebond 8360 12.2 12.8 104.9 Composition 1 19.3 18.4 95.3 Composition 219.3 9.9 51.3

TABLE 4 Moisture Resistance after HAST precondition on PLCC substrate(Die size: 80 × 80 mil; Substrate: PLCC silver coated copper leadframe)*HAST test: Expose unencapsulated specimen in 85% relative humidity and120° C. for 100 hr. and then pass solder reflow at 220° C. for 1 min.Die shear Die shear Adhesion strength before strength after retentionafter Material condition (kg) condition (kg) condition (%) JM2500 17.81.7 10.5 JM7100 2.8 4.4 157 JM2801 7.2 4.7 65.2 QMI505 12.4 10.5 84.7Ablebond 8360 12.1 8.6 71.1 Composition 1 19.9 16.6 83.4 Composition 219.4 3.7 19.1

TABLE 5 Moisture absorption after cure (Test condition: 2 hours inboiling water) Water absorption Material (%) JM2500 0.40 JM7100 0.09JM2801 0.95 QMI505 0.11 Ablebond 8360 0.48 Composition 1 0.11Composition 2 0.19

TABLE 6 Weight loss during curing Weight loss (%) Weight loss (%)Material (15-200° C.) (15-250° C.) JM2500 0.039 0.123 JM7100 0.092 0.118JM2801 0.104 0.173 QMI505 0.524 0.815 Ablebond 8360 3.883 5.022Composition 1 0.218 0.473 Composition 2 0.314 0.539

TABLE 7 Radius of Curvature (ROC) Comparison (Die size: 600 × 600 mil;Substrate: copper foil) ROC (m) ROC (m) Material Curing at 175° C./30min Curing at 150° C./60 min JM2500 1.6 1.8 JM7100 4.1 4.7 JM2801 0.330.38 QMI505 Delamination Delamination Ablebond 8360 0.39 0.41Composition 1 0.47 0.66 Composition 2 0.68 1.2

EXAMPLE 2

A third composition according to the invention was prepared usingdifferent process steps. The vehicle formulation involves eight parts,six of which are individual formulations. For each formulation, theamounts of each component are indicated as a weight percent based on thetotal weight of that formulation.

One or more dual functional molecules were used to crosslink the threemain functional groups (cyanate ester, epoxy, acrylic/vinyl) present inthe formulation. Crosslinking molecules that contain functionalitycommon to each group or that can be polymerized by any of the functiongroups present include MBXN327 (acrylic), EBC3604 (crossfunctionalizedwith acrylic and epoxy), UVA1562 (crossfunctionalized with acrylic andepoxy), V-CAP/RC (cross-functionalized with amines and vinyls), AY238(cross-functionalized with amines and epoxy), and aliphatic urethaneacrylates (cross-functionalized with amines and acrylates).

Part A—Formulation 1 dibenzoylmethane 12.0% zirconium 2,4-pentanedionate17.0% AKZ970 (Gelest, Inc., Tullytown, PA) neopentyl(diallyl)oxy &trineodecanoyl zirconate mixture  7.0% Ken-react NZ01 (KenrichPetrochemicals, Inc. Bayonne, NJ) epoxidized methyl linseedate 30.0%Vikoflex 9010 (Aldrich Chem. Co., Milwaukee, WI) cycloaliphatic epoxyresin 34.0% UVA 1501 (Radcure, Smyrna, Georgia)The components were all mixed together, and the mixture was heated to100° C. with mixing until all of the components were totally dissolved.The temperature was lowered to 60° C. The composition was mixed undervacuum until no more outgassing was observed. The formulation was thenstored at room temperature.

Part B—Formulation 2 boron trichloride amino complex 20.0% AcceleratorDY9577 (Ciba-Geigy, Brewster, NY) ethoxylated nonyl phenol acrylate20.0% SR504 (Sartomer Co., Exton, PA) epoxidized methyl linseedate 60.0%Vikoflex 9010 (Elf Atochem North America, Philadelphia, PA)The DY9577 was dissolved in the SR504 at 60° C., and the combination wasmixed under vacuum until no more outgassing was observed. The Vikoflex9010 was added at 60° C., and the resulting mixture was mixed undervacuum until no more outgassing was observed. The formulation was thenstored at room temperature.

Part C—Formulation 3 rubber modified epoxy acrylate blend diluted 20%50.0% with tripropylene glycol diacrylate Ebecryl 3604 (Radcure, Smyrna,Georgia) aliphatic urethane diacrylate diluted 10% with  5.0%N-vinyl-2-pyrrolidone Ebecryl 4834 (Radcure, Smyrna, Georgia)cyclohexanedimethanol divinyl ether 25.0% Rapi-cure CHVE (InternationalSpecialty Products, Wayne, NJ) bis[3,4-epoxy-cyclohexylmethyl-adipate]10.0% ERL4299 (Union Carbide, Danbury, Connecticut) conductive polymer10.0% Eeonomer P20-6F (Eeonyx Corp., Pinole, CA)All of the components were mixed together. The resulting slurry waspassed four times through a three roll mill, resulting in the producthaving a fog less than 2 microns and random streaks to 15 microns. Themixture was then heated to 60° C. and mixed under vacuum until no moreoutgassing was observed. The final viscosity of Formulation 3 wasapproximately 17,000 cps at 40 l/s. The formulation was stored at 0° C.

Part D—Formulation 4 aliphatic urethane diacrylate 60.0% Ebecryl 8402(Radcure, Smyrna, Georgia) aliphatic urethane acrylate 20.0% CN 980(Sartomer Co., Exton, PA) vinylcaprolactom mixture, 2H-azepin-2-one &1-ethylhexahydro 20.0% V-Cap/RC (International Specialty Products,Wayne, NJ)The components were mixed together, and the mixture was heated to 60° C.until the components were dissolved. The composition was mixed undervacuum until no more outgassing was observed. The formulation was storedat room temperature.

Part E—Formulation 5 cyclohexanedimethanol divinyl ether 7.0% Rapi-cureCHVE (International Specialty Products, Wayne, NJ) vinylcaprolactommixture, 2H-azepin-2-one & 1-ethylhexahydro 18.0%  V-Cap/RC(International Specialty Products, Wayne, NJ) cycloaliphaticepoxy/acrylate oligomer mixture 50.0%  Uvacure 1562 (Radcure, Smyrna,Georgia) hydantion epoxy resin: 2,4-imidazolidinedione-5-ethyl-5-methyl-1,3-bis(oxiranylmethyl)  19% Araldite AY 238 (Ciba-Geigy Corp.,Brewster, NY) pentaacrylate ester 6.0% SR9011 (Sartomer Co., Exton, PA)The components were mixed together and heated to 60° C. The compositionwas mixed under vacuum until no more outgassing was observed. Theformulation was stored at room temperature.

Part F—Formulation 6 1,1-bis[4-cyanatophenyl]ethane 54.5% AroCy L-10(Ciba Geigy, Brewster, N.Y.) methacrylated polybutadiene acrylonitrile17.0% Echo Resin MBXN327 (Echo Resin, Versailles, MI)cyclohexanedimethanol divinyl ether 28.0% Rapi-cure CHVE (InternationalSpecialty Products, Wayne, NJ) nadic methyl anhydride, methylene4-endomethylene-  0.5% tetrahydrophthalic anhydride Hardener HY 906(Ciba-Geigy Corp., Brewster, NY)The AroCy L-10 and MBXN327 were mixed together. The combination washeated to 60° C. and mixed under vacuum until the components weredissolved. The temperature was lowered to 25° C. The HY 906 and CHVEwere added. The composition was mixed under vacuum at 25° C. until nomore outgassing was observed. The formulation was stored at 0° C.Part G—Formulation 7

The above formulations were combined to form formulation 7 as follows.

Formulation 1 12.0%

Formulation 2 2.0%

Formulation 3 7.0%

Formulation 4 25.8%

Formulation 5 17.0%

Formulation 6 35.0%

HY 906 0.7%

Vinyltrimethoxysilane 0.5%

Formulations 3, 4, 5, and 6 were mixed together. The resulting mixturewas heated to 40° C. and mixed under vacuum until no more outgassing wasobserved. The mixture was then cooled to 15° C. Formulation 2 was thenadded, followed 10 minutes of mixing. Formulation 1 was then added,followed by another 10 minutes of mixing. HY 906 was added, followed byan additional 10 minutes of mixing. The temperature of the mixture wasraised to 25° C. Vinyltrimethoxysilane was added, followed by 30 minutesof mixing under vacuum. The resulting composition was stored at 0° C.for one week.

Part H—Complete Formulation

The final die attach formulation comprised two parts: the formulatedvehicle (Formulation 7) and filler.

Formulation 7 19.5%

Silver filler 80.5%

The temperature was set at 15° C. The silver filler and Formulation 7were mixed together for about 15 minutes under vacuum. The temperaturewas raised to 25° C., followed by 45 minutes of mixing under vacuum. Thecomposition was transferred to a cartridge with a ram press, and thecartridge was vacuumed for about 20 minutes. The final formulation wasput into syringes and stored at −40° C.

The physical properties of composition 3 were tested, as listed in Table8. Filler (silver) 80.5% Viscosity 7.1 Pas Pot life 24 hrs. Recommendedcure profile 175° C./30 min or 150° C./1 hr Electrical volumeresistivity 0.0007 ohm-cm Die Shear Strength 15 kg on Ag spot (80 × 80mil die) Cu PLCC leadframe Die Shear Strength 60 kg on Ag spot (200 ×200 mil die) Cu PLCC leadframe Water absorption 0.6% (in 100° C. boilingwater for 2 hrs) Glass Transition Temperature (DMA 142 C. method)Young's Modulus 2.5 Gpa ROC 0.8 m (600 × 600 mil die on Cu foil)Coefficient of thermal expansion 44--m (T < Tg) 136 ppm (T > Tg) Storagelife (at −40° C.) 6 months

It is apparent from the foregoing that various changes and modificationsmay be made without departing from the invention. Accordingly, the scopeof the invention is limited only by the appended claims, wherein what isclaimed is:

1-93. (canceled)
 94. A composition comprising an organic component and afiller, wherein the organic component comprises: at least one long-chaincycloaliphatic epoxy resin, at least one short-chain cycloaliphaticepoxy resin, at least one cyanate ester, at least one Lewis acidcatalyst, and at least one flexibilizing modifier.
 95. The compositionof claim 95, wherein the composition further comprises at least oneBronsted acid co-catalyst.
 96. The composition of claim 96, wherein theat least one Bronsted acid co-catalyst is a weak Bronsted acid catalyst.97. The composition of claim 95, wherein the at least one Bronsted acidco-catalyst comprises phenol-based molecules, diketonates, diesters orketoesters.
 98. The composition of claim 95, wherein the at least oneBronsted acid co-catalyst is present in an amount ranging from about0.3% to about 0.8% by weight based on the total weight of the organiccomponent.
 99. The composition of claim 94, wherein the at least oneflexibilizing modifier comprises at least one functionalized flexiblelong-chain compounds.
 100. The composition of claim 99, wherein the atleast one functionalized compound comprises epoxy-terminated siloxanes,epoxy/hydroxy functionalized polybutadiene, epoxidized oils, long-chainfunctionalized double bond compounds or a combination thereof.
 101. Thecomposition of claim 100, wherein the epoxidized oils compriseepoxidized methyl linseedate.
 102. The composition of claim 100, whereinthe long-chain funcationalized double bond compounds comprise acrylates,rubbers or a combination thereof.
 103. The composition of claim 102,wherein the acrylates comprise urethane acrylates or methacrylatedpolybutadiene acrylonitrile.
 104. The adhesive of claim 94, wherein saidat least one long-chain cycloaliphatic epoxy resin is selected from thegroup consisting of cycloaliphatic mono- and di-epoxy oligosiloxanes.105. The adhesive of claim 94, wherein said at least one long-chaincycloaliphatic epoxy resin is selected from the group consisting ofbis[3,4-epoxy-cyclo-hexyl-methyl]adipate, epoxidized α,ω-di-(3,4cyclohexene-2-ethyl)-tetramethyl disiloxane, epoxidizedα,ω-di-(3,4-cyclohexene-2-ethyl-hexamethyl trisiloxane, and epoxidizedα-3,4-cyclohexene-2-ethyl pentamethyldisiloxane.
 106. The adhesive ofclaim 94, wherein said at least one long-chain cycloaliphatic epoxyresin is present the composition in an amount ranging from about 5% toabout 20% by weight based on the total weight of the organic component.107. The adhesive of claim 94, wherein said at least one long-chaincycloaliphatic epoxy resin is present the composition in an amountranging from about 12% to about 15% by weight based on the total weightof the organic component.
 108. The adhesive of claim 94, wherein said atleast one short-chain cycloaliphatic epoxy resin has a short chainbetween the cycloaliphatic groups containing 2 or less carbon atoms.109. The adhesive of claim 94, wherein said at least one short-chaincycloaliphatic epoxy resin is selected from the group consisting of3,4-epoxy-cyclohexylmethyl-3,4-carboxylate, vinyl cyclohexene dioxide,and 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy) cyclohexanemeta-dioxane.
 110. The adhesive of claim 94, wherein said at least onecyanate ester has two or more isocyanate functional groups.
 111. Theadhesive of claim 94, wherein said at least one cyanate ester comprises1,1′-bis[4-cyanatophenyl]ethane,bis(4-cyanato-3,5-dimethylphenyl)methane, and1,3-bis(cyanatophenyl-1-(1-methylethylethylidene))benzene.
 112. Theadhesive of claim 94, wherein the Lewis acid catalyst comprises acompound selected from the group consisting of titanium-based compounds,organo-tin compounds, zirconium-based compounds, tantalum-basedcompounds, vanadium-based compounds, boron-amine complexes, boroncomplexes, boron halides, amino complexes of boron halides, and aluminumhalides.